1. Field
Embodiments relate to high selectivity, low noise front end receivers for a remote radio head receiver or a distributed base station receiver.
2. Description of the Related Art
Recently, the FCC has reallocated the 698-746 MHz (lower 700 MHz band) that had been allocated to television channels 52-59. Licensees of the lower 700 MHz band have a challenge to overcome before practical use of the lower 700 MHz band can be utilized. The surrounding frequency bands (e.g. 614-698 MHz and 716-722 MHz) are used by popular and emerging technologies (e.g., Digital Television and the MediaFLO Standard (FLO TV)).
FIG. 1 illustrates a typical distributed wireless base station system 100. As shown in FIG. 1, a base station receiver 110 is connected to a core network 105. Base station receivers 110 and core networks 105 are known in the art and will not be described for the sake of brevity. The base station receiver may receive a signal from, for example, a tower mount antenna 120, a rooftop antenna, and/or a wall mount antenna 130.
As is known in the art, the tower mount antenna 120, the rooftop antenna, and/or the wall mount antenna 130 may receive a signal from, for example, a mobile phone (not shown). In order to conserve power, signals transmitted by, for example, mobile phones are lower power signals. Unfortunately low power signals are susceptible to interference from other more powerful signals.
Under ideal conditions, any receiver will perform well. However, if site noise is not ideal, received signals are not strong and off-channel signals are strong, the selectivity of a receiver and the design of an amplifier become relatively important.
The lower 700 MHz band does not operate under ideal conditions. As described above, the lower 700 MHz band is at least susceptible to strong off-channel signals.
Referring again to FIG. 1. As shown in FIG. 1, the typical distributed wireless base station system 100 also includes an interference mitigation block 115. The interference mitigation block 115 is electrically between the receive antenna (e.g., tower mount antenna 120) and the base station receiver 110.
The interference mitigation block 115 selectively filters the off-channel signals (e.g., Digital Television channel 51 and the MediaFLO Standard (FLO TV)) and amplifies the signal received from the antenna. Typical requirements for the interference mitigation block 115 are, for example, shown in table 1 below.
TABLE 1ParameterSpecificationRejection40 dBPass band698.3 MHz-715.7 MHzStop Band697.8-716.2Noise figure~1 dB over 80% of pass bandLinearityHigh IP3
The only existing solution for an interference mitigation block to meet the above specifications is illustrated in FIG. 2. As shown in FIG. 2, the interference mitigation block 200 includes a cryogenic cooler 210, a cryogenically cooled enclosure 215, a high order, very high Q-factor RF Filter 220 and a very low noise figure amplifier 225.
The cryogenic cooler 210 in combination with the cryogenically cooled enclosure 215 keep the surroundings of the filter 215 and the low noise amplifier 225 to a temperature of less than 100K. By keeping the surroundings to less than 100K, the filter 215 and the low noise amplifier 225 achieve superconducting properties and thus are able to perform to the specifications listed in table 1, for example. Filter 220 may receive a signal from antenna 205 and selectively pass frequencies in the pass band of the interference mitigation block 200.
As one skilled in the art will appreciate, the drawbacks of the existing solution of using the interference mitigation block 200 as shown in FIG. 2 are numerous. Not the least of which is the cost of every system using cryogenics. Further, the system reliability of cryogenically cooled systems is limited. Two reliability limitations are, for example, DC power consumption, and “start up” time. If a power failure occurs, the cryogenically cooled system draws on batteries so the system may go down faster, and the cryogenically cooled system requires considerable time to start up again as it takes time to cool the system after the power comes back on. System reliability issues are critical today as people rely on wireless systems as their primary connection, including, for example, emergency situations.
Residents of these buildings may be leery of a building having a liquefied gas tank. Each of the cryogenic coolers 210 will require tank refills on a regular basis. Remote cryogenic coolers 210 will need to be monitored in some manner. The ongoing expense of using the interference mitigation block 200 as shown in FIG. 2 will continue to mount as more systems are put in use and as the lifetime of these systems increase.
Further, there are only a limited number of suppliers for such cryogenically cooled superconducting filters. Still further, the reliability of a cryogenically cooled filter is relatively low as is known based on typical mean time between failure calculations.